Conventionally, there is known a sealing device such as an oil seal that includes a main lip that prevents leakage of a target liquid to be sealed such as oil, and a dust lip that prevents intrusion of a foreign object such as dust into a sealed area from the outside. With this sealing device, it is possible to seal an annular gap between a shaft and a housing.
In the sealing device, the tip of the shaft hits the dust lip when the shaft is inserted into the sealing device, whereby there are cases where the dust lip is turned over or damaged. This respect will be described with reference to FIG. 14. FIG. 14 is a schematic cross-sectional view of the sealing device of a conventional example. FIG. 14 shows a state when the shaft is inserted into the sealing device.
A sealing device 500 shown in the drawing includes a reinforcing ring 510, and a seal main body 520 made of a rubber-like elastic body that is provided integrally with the reinforcing ring 510. In addition, the seal main body 520 integrally includes a main lip 521, a dust lip 522, a side lip 523, and an outer peripheral sealed portion 524. According to the sealing device 500, it is possible to prevent leakage of the target liquid to be seal to the side of the dust lip 522 using the main lip 521, and prevent intrusion of a foreign object to the side of the main lip 521 using the dust lip 522. In the sealing device 500, when the sealing device 500 is assembled, a shaft 200 is inserted from the side of the dust lip 522 to the side of the main lip 521 (a direction of an arrow A in the drawing). At this point, the tip of the shaft 200 hits the dust lip 522, whereby there are cases where the dust lip 522 is turned over or damaged.
Note that a technique for solving the above problem is also known (see PTLs 1 to 4). However, in the technique disclosed in PTL 1, a protector for protecting the dust lip is made of metal, and hence there is a possibility that the shaft itself is damaged. In the case of the technique disclosed in PTL 2, when the shaft hits a guide ring, the base of the dust lip is pushed by the guide ring so that there is a possibility that the dust lip is significantly deformed. Note that the guide ring disclosed in PTL 2 is provided not for preventing the shaft from hitting the dust lip when the shaft is inserted originally. Further, in the case of the techniques disclosed in PTLs 3 and 4, the inner diameter of a protection member (guide member, protector) for protecting the dust lip is configured to be smaller than the outer diameter of the shaft, and the protection member is configured to come into contact with the shaft. Accordingly, there is a possibility that an insertion force required to insert the shaft is uselessly increased, or deformation of the protection member itself causes a problem. Thus, there is yet room for improvement.